Metal castings are made by pouring molten metal through a gating system into a casting assembly made of molds and cores. The molds and cores are typically made by shaping a mixture of a foundry aggregate, e.g. sand, and a foundry binder. When the molten metal is cooled, the metal casting is separated from the molds and cores and any excess aggregate and binder are removed from the casting.
Molten metal used to produce metal castings typically contains contaminants, e.g. metal oxides. Filters are used extensively in the foundry industry to filter contaminants found in molten metal. Typically the filter is made from ceramic materials that are formed by extrusion, pressing, or by impregnating a ceramic slurry into a foam. The shape is dried in an oven and fired in a kiln oven to cure the filter.
Patents describing various filters used in the foundry industry include U.S. Pat. No. 6,468,325 (making and firing in a kiln to for a filter), U.S. Pat. No. 6,296,794 (pressed porous filter bodies), U.S. Pat. No. 5,961,918 (honeycomb extruded filter), U.S. Pat. No. 5,190,897 (ceramic foam filter), U.S. Pat. No. 5,104,540 (filter with a carbon coating to minimize thermal shock to the filter), and U.S. Pat. No. 4,921,616 (alveolar ceramic filters for high melting metals).
Most of the filters described in these patents describe design changes to improve the filtering of tramp particles out of the liquid metal. The focus of the design is on the ability of the filter to trap small particles in the metal that could become a defect in the casting. Manufacturing costs, removal from the gating system, metal contamination by the filter itself, and design flexibility are not significantly addressed.
Furthermore, filters typically used in the foundry industry are hard to prime because of their mass and the relatively short time required to pour a casting. This is because filters require a large amount of heat to bring them up to the temperature of the metal. The heat needed to prime the filter comes from the molten metal, which in turn also cools the metal at a rapid rate.
There is also a problem with pieces of the filter getting back into the furnace when the metal from the gating system is re-melted. The filters become impregnated with metal and remain in the gating. When the gating system is returned to the furnace for re-melting small pieces of the filter can get trapped in the furnace and stay in the metal when it is poured potentially causing casting defects. Therefore, it is customary to remove the pieces of the filter from the molten metal in the furnace.
All citations referred to in this application are expressly incorporated by reference.